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HBA2 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

HBA2 gene

The HBA2 gene provides instructions for creating alpha-globin, a critical protein subunit of hemoglobin that enables red blood cells to transport oxygen throughout the body.

Normal Function

The HBA2 gene provides instructions for making a protein called alpha-globin. This protein is also produced from a nearly identical gene called HBA1. These two alpha-globin genes are located close together in a region of chromosome 16 known as the alpha-globin locus.

Alpha-globin is a component (subunit) of a larger protein called hemoglobin, which is the protein in red blood cells that carries oxygen to cells and tissues throughout the body. Hemoglobin is made up of four subunits: two subunits of alpha-globin and two subunits of another type of globin. Alpha-globin is a component of both fetal hemoglobin, which is active only before birth and in the newborn period, and adult hemoglobin, which is active throughout the rest of life.

Each of the four protein subunits of hemoglobin carries an iron-containing molecule called heme. Heme molecules are necessary for red blood cells to pick up oxygen in the lungs and deliver it to the body's tissues. A complete hemoglobin protein is capable of carrying four oxygen molecules at a time. Oxygen attached to hemoglobin gives blood its bright red color.

Health Conditions Related to Genetic Changes

Alpha thalassemia

Deletions of the HBA1 and/or HBA2 genes are the most common cause of alpha thalassemia. Less commonly, variants (also called mutations) in or near these genes cause the condition. The signs and symptoms of alpha thalassemia tend to be more severe when the disease results from variants in the alpha-globin genes than when it is caused by deletions of these genes.

People have two copies of the HBA1 gene and two copies of the HBA2 gene in each cell. Each copy is called an allele. For each gene, one allele is inherited from a person's father, and the other is inherited from a person's mother. As a result, there are four alleles that produce alpha-globin. The different types of alpha thalassemia result from the loss of some or all of these alleles.

  • Hb Bart syndrome: The most severe form, resulting from the loss or alteration of all four alpha-globin alleles. It is characterized by a buildup of excess fluid in the body before birth (hydrops fetalis), a shortage of red blood cells (anemia), and an enlarged liver and spleen (hepatosplenomegaly).
  • HbH disease: A milder form usually caused by a loss of three of the four alpha-globin alleles. It is characterized by mild to moderate anemia, hepatosplenomegaly, and yellowing of the eyes and skin (jaundice).
  • Alpha thalassemia trait: A loss of two of the four alpha-globin alleles. People with this trait may have unusually small, pale red blood cells and mild anemia.
  • Alpha thalassemia silent carriers: A loss of one alpha-globin allele. These individuals typically have no thalassemia-related signs or symptoms.

Other disorders

A condition called alpha-thalassemia-intellectual disability syndrome, chromosome 16-related (ATR-16) results from a large deletion of genetic material from the short (p) arm of chromosome 16. The loss of many genes, including HBA1 and HBA2, leads to features including:

  • Alpha thalassemia trait
  • Intellectual disability
  • Severely delayed language skills
  • Unusually small head size (microcephaly)
  • Distinctive facial features
  • Undescended testes (cryptorchidism) and hypospadias in affected males

Other Names for This Gene

  • alpha 2 globin
  • alpha globin
  • alpha-2 globin
  • alpha-globin locus, second
  • HBA-T2
  • HBA_HUMAN
  • hemoglobin, alpha 2
  • hemoglobin-alpha locus 2
  • major alpha-globin locus

Frequently Asked Questions

Yes. Point mutations or small insertions/deletions in HBA2 can reduce or abolish alpha‑globin production. These variants often produce a milder form of alpha‑thalassemia than large deletions, but they can still lead to anemia, splenomegaly, or other complications depending on how many functional alpha‑globin genes remain.
Being a carrier means you have one normal copy of the HBA2 gene and one deleted copy. You typically have no symptoms because the other alpha‑globin gene (HBA1) and the other HBA2 copy can produce enough alpha‑globin to keep hemoglobin levels normal. However, if you have a partner who is also a carrier, there is a 25 % chance with each pregnancy that the child will inherit two deleted copies and develop alpha‑thalassemia trait or disease.
Diagnosis usually starts with a complete blood count showing microcytic, hypochromic anemia. If alpha‑thalassemia is suspected, a molecular test such as multiplex ligation‑dependent probe amplification (MLPA) or gap‑PCR is performed to detect deletions in HBA1 and HBA2. Hemoglobin electrophoresis can also help by showing reduced or absent HbA2 and HbH (beta‑globin tetramers).
Treatment depends on severity. Mild cases may only need iron‑free supplements and regular monitoring. Moderate to severe cases often require regular blood transfusions to maintain hemoglobin levels, followed by iron chelation therapy to prevent iron overload. In some families, hematopoietic stem‑cell transplantation or gene‑therapy approaches are being explored as curative options.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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